Your hair falls out during chemotherapy treatment because of the damage done to the hair follicle by the chemo drugs. Chemotherapy destroys rapidly dividing cells in the body, but it cannot differentiate between unhealthy cells, such as those in a cancerous tumor, and those that are healthy, such as those in the hair follicles. The damage caused to the hair follicle by the chemo drugs will cause hair loss, usually starting between 14 and 21 days after the first chemotherapy infusion. Scalp cooling protects the follicle and helps to reduce hair loss ensure faster hair regrowth.